Polymerization of conjugated diene hydrocarbons



Patented July 31, 1945 POLYMERIZATION F OONJUGATED DIENE HYDROCABBONSGeorge L. Browning, Jr., William Benjamin M. G. Zwicker, Akron, on, bymesne assignments, 'to 'lh D. Stewart, and

rich Company, Akron, Ohio, a corporation of New York No Drawing.Application May 31, 1941, Serial No. 396,156

8 Claims.

This invention relates to the polymerization oi butadiene hydrocarbonsand particularly to a method whereby butadiene hydrocarbons may bepolymerized in aqueous emulsion to form products closely resemblingnatural crude rubber.

It is disclosed in the copending application of Charles F. Fryling,Serial No. 396,155, filed May 31, 1941, that compounds containing. a 2-thiothiazyl group modify the emulsion polymerization or butadienehydrocarbons in such a manner that polymers more nearly resemblingnatural rubber are produced. We have discovered that an additionaleflect is obtained by conducting the polymerization in the presence of asmall amount of a simple ionizable nickel salt, namely that the timerequired to form a homogenous sheet when the polymer is worked on a rollmill,

herein called the "breakdown time, is greatly shortened. This effect isnot obtained when the polymerization is eflected in the presence ofcertain other well-known modifiers, or when certain other simpleionizable salts of certain other heavy metals are employed.

Any modifier containing the 2-thiothiazyl group which may be representedby the following structural formula:

l Er --s 6 1 as great activity as the aliphatlc-z-mercapto thiazolesinclude the aromatic thiazoles, by which is meant compounds in which thecarbon atoms numbered 4 and 5 form part oi an unsaturated carbocyclicring. such as z-mercaptobenzothiazole, Z-mercapto-naphthothiazole, andthe corresponding aromatic bis-thiazyl-z mono-, di-, and

des. z-thiazyl sulfides such as 4,5-dimetbylthiaryl-2 diethylaminosulfide, benzothiasyl-2 dicyclohexylamino sulfide, and other compoundscontaining the il-tbiazyl group may also be cmvloyed.

The proportion in which the 2-thiothiazyl compound is included in thecomposition depends somewhat upon the properties desired in the product,the higher proportions of modifier-in general producing softer, moresoluble polymers. Very small amounts of modifier such as 0.1% or evenless based on the monomers in the emulsion may profoundly aflect thenature of the polymer produced, and amounts up to 5% or over pound bycoordinated covalences and is meant to include only those compounds inwhich the metal exerts its primary positive valences.

Among the simple ionizable nickel salts which may be employed may bementioned the chlorides,

g5 bromides, nitrates, sulfates, carbonates, borates,

acetates, sulfites, thiosulfates, cyanides, and sulfides, thewater-soluble salts including the halides, sulfates, and nitrates beingpreferred. It is generally desirable to employ the nickel salt inamounts not greater than .1% based on the monomers, although this is nota critical value, and amounts as great as 1% and more may be used insome instances, some systems exhibiting a greater tolerance towardsexcess nickel salt than others. The use or too great amounts of nickelsalt will increase the time required tor the polymerization to reachcompletion.

As a specific example of the methodoi this invention, parts by weight oibutadiene and 45 parts of acrylonitrile were copolymerized at 30 C. inthe presence or about 250 parts of a 8% solution of fatty acid which hadbeen neutralized with sodium hydroxide, 0.35 part or hydrogen peroxideas an initiator, and 1 part oi. 2- mercapto-4,5-dimethylthiazole as amodifier. By coagulation of the latex-like product oi thepolymerization, a coherent, plastic material was obtained. It was foundthat it required 13 minutes before the polymer formed a coherent,plastic sheet on a roll mill. When the polymerization was performed inthe presence 01 0.01 part oi nickel sulfate, however, a soft, plasticpolymer which had a breakdown time of only 5 minutes was obtained.

The modifying agents or this invention my polymerization.

be employed in the polymerization in aqueous emulsion of butadienehydrocarbons such as butadiene, 2,3-dimethylbutadiene,v isoprene, orpiperylene either alone or in admixture with each other or with othermonomers copolymerizable therewith.

As examples of monomers copolymerizable with butadiene hydrocarbons maybe mentioned such compounds as styrene, vinyl naphthalene,

acrylonitrile, methacrylonitrile, methyl methacrylate, vinyl acetate,vinylidene chloride, methyl vinyl ketone, methyl vinyl ether. andsimilar unsaturated hydrocarbons, nitriles. esters, ketones, and ethers.These monomers are preferably employed in smaller amounts than thebutadiene hydrocarbons.

- The polymerization of the above materials in aqueous emulsion may beeffected by various initiators of polymerization such as per-compoundsincluding per-acidsperoxides, and persalts such as persulfates,perborates, percarbonates, andthe like, as well as other types ofinitiators such as di'azoaminobenzene, and dipotassium diazomethanedisulfonate.

Any of the ordinary emulsifying agents such as fatty acid soapsincluding sodium oleate and sodium stearate, hymolal sulfates and arylsulfonates including sodium lauryl sulfate and sodium isopropylnaphthalene sulfonate; and salts of organic bases containing long carbonchains such as the hydrochloride of diethylaminoethyloleylamlde,trimethylcetylammonium methyl sulfate, etc., may be employed in the Theterms butadiene hydrocarbo and a butadiene hydrocarbon signifybutadiene-1,3 and its homologues which enter into polymerizationreactions in substantially the same manner. The term sulfide" is ageneric term including the mono-, di-, and polysulfldes.

. Although we have herein disclosed specific embodiments of ourinvention, we do not intend to limit the invention solely thereto, forit will be obvious to those skilled in the art that many variations andmodifications are within the spirit and scope of the invention asdefined in the appended claims.

We claim:

1. The method which comprises polymerizing a conjugated butadienehydrocarbon in the form of an aqueous emulsion in the presence of acompound containing the z-thiothiazyl group and a simple ionizablenickel salt.

2. --'1'he method which comprises polymerizing a conjugated butadienehydrocarbon in the form of .an aqueous emulsion in the presence of a 2-mercaptothiazole and a water-soluble nickel salt.

3. The method which comprises copolymerizing in the form of an aqueousemulsion butadiene and a smaller amount of a monomer copolymerizabletherewith in aqueous emulsion in the presence of a Z-mercaptothiazoleand less than 0.1% based on the materials polymerized of a water-solublenickel salt.

4. The method which comprises copoLvmerizing butadiene andacryloniti'ile in the form of an aqueous emulsion in the presence of analiphatic 2-mercaptothiazole and less than 0.1% based on the materialspolymerized of a water-soluble nickel salt.

5. The method of claim 4 in which 2-me1- capto-4,5-dimethyl 'thiazole isemployed.

6. The method which comprises polymerizing a conjugated butadienehydrocarbon in the form of an aqueous emulsion in the presence of ahisthiazyl-2 sulfide and less than 0.1% based onthe material polymerizedof a water-soluble nickel salt.

7. The method which comprises copolymerizing butadiene and acrylonitrilein the form of an aqueous emulsion inthe presence of an aliphaticbis-thiazyl-2 disulilde and less than 0.1%

based on the materials polymerized of a watersoluble nickel salt.

8. The method which comprises polymerizing a conjugated butadienehydrocarbon in the form of an aqueous emulsion in the presence of acompound containing the 2-thiothiazyl group and less than 0.1% based onthe material polymerized of nickel sulfate.

GEORGE L. BROWNING, JR. WILLIAM D. STEWART. BENJAMIN IM. G. ZW'ICKER.

